Ventilation of a patient involves the delivery of a breathable gas (typically ambient air to which a complementary gas such as oxygen can be added) pressurised above atmospheric pressure to a patient via a conduit, and a mask or tracheotomy tube.
There are more and more troubles that require assisted and/or controlled ventilation of the patient. It is namely common to use breathing assistance devices for diseases where mechanical ventilation is needed, for example in neuromuscular disease where volume controlled ventilation is required. These devices may also be used for other respiratory diseases or disorders, such as for the continuous positive airway pressure (CPAP) treatment of obstructive sleep apnea.
For either application of assisted and/or controlled ventilation, the pressure of the gas delivered to patients can be constant level, bi-level (in synchronism with patient breathing) or auto-adjusting in level. Further, some troubles require feeding the patient with a controlled volume of breathable gas, such as for neuromuscular patients. Throughout this specification reference to gas supply unit is intended to incorporate a reference to any one of, or combinations of, these forms of pressurised gas supply.
A disadvantage of existing gas supply units is the danger of biological contamination and disease/virus/bacteria transfer. More particularly, there can be a significant reverse flow during heavy expiration and/or coughing and biological material exhaled by a patient can be deposited in the gas supply unit. In this case, a patient continually using the same machine can be re-infected by a prior condition, or the deposited biological material may be transferred to another patient who uses the same machine.
A gas supply unit generally comprises a closed outer casing surrounding internal components. Components inside, and constituting part of, the gas flow path include for instance the gas inlet, inlet filter, impeller, and gas outlet. Components outside the gas flow path include control electronics, power regulators and motor. As a result, such gas supply units have a gas flow path that is extremely difficult to clean/sterilise without the time consuming dismantling and removal of all the “gas flow path” components. Further, without disassembly, common sterilisation procedures such as autoclaving will damage the circuit boards and other electrical components.
As a consequence, gas supply units have been developed to overcome this problem in separating the components inside the gas flow path from the outside components. In the United States Patent published on Oct. 16, 2001 under the reference U.S. Pat. No. 6,302,105, Wickham et al. have for example proposed a gas supply unit with a main housing for the components outside the gas flow and a sub-housing for the components inside the gas flow. However, for complete independence of the sub-housing from the main housing, coupling of the inside and outside components is relatively complex and increases the size of the gas supply unit. This is especially true for gas supply units enabling treatment of serious respiratory troubles. Such increase in the size of the unit is disadvantageous in view of the preference for miniaturization of breathing assistance devices for improving the patient's comfort. Furthermore such devices do not enable feeding a patient with a controlled volume of breathable gas which may be required for some specific treatment.
Therefore, it is an object of the present invention to provide a gas supply unit that substantially overcomes or at least ameliorate one or more of the above deficiencies.